With the development of the Internet, a great deal of information is on-line. Popular search sites could be visited million times daily and the sites related to your interest will often be visited by you. Although bookmarks can be used to record frequented Web sites, browsers discard most history and trail information. The explosion of information needs a more effective mechanism. Memex has been considered in this domain. Assisted by Memex, a Web surfer can retrieve the URL trails that a user visited several months ago. In this paper, we propose a mechanism Self-modifiable Color Petri Net - SCPN to simulate the Memex functions in a Web browser. In this mechanism, an SCPN instance is used to record a trail of a topic, a place in an SCPN instance represents a Web site.